Safety device for electric heaters



May 27, 1930. L. P. HYNES ,7

SAFETY DEVICE FOR ELECTRIC HEATERS Filed May 9, 1923 4000 -OHMS Qgvvucutoz LEE P. HYNE5 9.51 1 1% lbtmm Patented May 27, 1930 warrensTATns PATENT err-ice LEE 2. 8, Oi ALBANY, NEW YORK, ASSIGNOR, BY MESNEASSIGNMENTS, TO CON- SOLIDATBD CAB-HEATING COMPANY, INC., OF ALBANY, NEWYORK, A CORPORATION or nnwxonx ear-1m! nnvrcr. ron nrnc'rnrc rmArnnsApplication med May 9, 1923. Serial No. 37,843.

For a detailed description of the present form of my invention,reference may be had to the following specification and to the ac.-companying drawing forming a part thereof.

My invention relates to safety devices for electric heaters and isillustrated by the accompanying drawing.

It is customary in electric railway cars, because of the voltage used,to place the several heaters in the car in series and to rely on a fuseto protect the heater circuit. The most common accidents are thebreaking of a heater coil, a loose connection, or the insertion of aforeign piece of metal or wire. These and other causes occasion agrounding of the heater circuit at some point along its length. Thiswill short circuit one or more of the series of heaters and cause anabnormal How of current in those which are not short circuited. Even ifit occurs near the ground, it may not seriously overload the heaters butis likely to cause flashing to the case with danger to passengers andthe car. Hence it is uncertain whether, in the case of accident, therewill or will not be a suiiicient amount of current in the heater circuitto blow the fuse, while it is also necessary to allow a considerablemargin in fusing on' account of the high temperature coeflicient on someof the heater elements now used. For this reason fuses have become aninadequate means of protection for electric heaters, while otherprotective devices, dependent on the rise in current value, are sub ectto similar uncertainties. In addition, there is such a variety ofamperage in difierent heater circuits that it would take carefulfiguring to get the right setting on such a device for differentinstallations and for difierent circuits in any one installation,

and it is also quite possible that a broken wire near ,the ground wouldreduce an are which would even decrease rat er than increase the amerage.

o overcome these dilficulties, I have devised a protector dependent onthe differential magnetic action of coils located at the respective ndsof the heater circuit. By this means any difference in the amperage atthe opposite ends of that circuit, regardless of what the total amperagemay be, will serve to set in action some appropriate cut-out agency thatwill break the heater circuit. I prefer to utilize as such a cutting-outagency the automatic switch that is dominated by the car thermostat inmaintaining a given temperature in the car.

Referring to the drawing, the members 1 to 8 indicate eight electricheaters connected in series in the heater circuit a which goes fromtrolley T by way of blow-out coil 14, switch M to ground at G. Beforethis circuit reaches the heaters, after passing through the usual fuse18, it passes through a magnet coil X and after it leaves the heaters itpasses through the magnet coil Y which is wound on the same core as coilX but in the opposite direction. Coils X and Y' are wound'of large wirethat will carry the heater current continuously without heating. So longas the heatin circuit is intactthe same current will pass t rough bothcoils, which will neutralize each other and the magnet will remaininactive. If, however, there should be an accidental ground on thecircuit-say at the point Z-a greater or less portion of thecurrent-would be diverted from coil Y which would then be overpowered bycoil X. The magnet would then be energized and attract its armature C.Also if an accidental connection should be established between theterminals of coil X it would cause coil Y to act, While an accidentalshort-circuiting of both coils wculd he certain to blow the fuse. Ineither event the heaters would be cut oil.

M is the main switch for the heater circuit and is operatedautomatically by the thermostat D. The switch is held open by aretracting spring H so long as the car is heated to the predetermineddegree, but is automatically closed when the temperature falls belowthat de ree. From the trolley T a shunt circuit d of about 4000 ohms,assumin that the trolley voltage is about 550, to the ranchin point W.Thence a'branch da goes throug magnet K, of about 900 ohms resistance toground at 9 and a second branch db goes through thermostat D to groundatlO. The ther mostat is preferably of the mercury type and when thetemperature is up it closes branch circuit db and thereby short-circuitsmagnet K which allows that magnet to release'its armature and openswitch M. When the temperature is down the thermostat breaks branchcircuit db, thereby removing the short circuit from magnet K. The magnetis thereby energized and attracts its armature closing the heater switchM. To this arrangement, which is old and well known, I add a thirdbranch circuit dc which is controlled by the aforesaid differentialaction of the coils X and Y in a way like to the control of the branchcircuit db by the thermostat D. The core on which coils X and Y arewound is provided with an armature C, which projects under the lower endof a rod P which is pressed down by a spring Q. The upper end of P bearsagalnst the outer end of a latch R which engages a shoulder on theindicator lever S and locks it against the rotating force of a spring J.The lever S is grounded, the ground connection being indicated at 8.-

Assumin that the equality of ma netizing effect of 001 s X and Y isdisturbed y an accidental ground on the heater circuit as abovedescribed, one of the two coils will preponderate and energize the core.The armature C will then be attracted, lifting rod P, tripping latch Rand allowin lever S to rotate into contact with a stop which constitutesthe terminal of the aforesaid branch circuit dc. The result will be theshort-circuiting of magnet K of the master switch M, just as it isshort-circuited when the branch db is closed by thermostat D. Magnet Kwill then release its armature and break the heater circuit. Thereleased position of lever S is shown in dotted lines. In this positionthe top plate of lever S, which is colored red, is brought into avertical position in front of window 16. Thereby an observation of theapparatus, without openin the box, will show that it has acted, andlfmore than one such apparatus is contained in the same box, it willshow which one has acted. In some cases there are two or more heatercircuits in the same car and I .have indicated at b a second heatercircuit in parallel with the circuit a. and controlled by the samemaster switch M.

This circuit b may have its own individual set of coils'X and Y withassociated arts contained in the same box with those 0 circuit a. Ifeither one of these two circuits is accidentally grounded, both circuitswill be broken.

goes through a resistance F That will more quickly call attention, by adrop in temperature which the thermostat fails to correct, to the factthat the emergency cut-out has acted, provided that such action was notnoticed at the time it occurred. The box will be locked, but anauthorized ins ector will unlock it, after the action takes p ace, andwill reset it by simply turning lever S back to its vertical position.That will break the short-circuit established by circuit dc of themaster switch magnet K which will close and admit current to the heatercircuit before lever S reaches its upright position. If the accidentalground on the heater circuit still remains, the latchR will not act andlever S will not stay in its lifted position. That will show that theheaters can not be used. But if the ground has disappeared the lever Swill be atched and remain upright, the heaters being then in workablecondition.

I also provide a grounding push-button 5, by which the circuit dc may bemanually grounded. By this means the car conductor or other person canturn the heaters off or on at will merely by pushing in or drawing outthe button 5 without resort to the large heavyduty switches ordinarilyemployed for that purpose. When he pushes in the button 5 he does notdisturb in any way the cut-out apparatus, but grounds out ma et K justas the thermostat does when it c oses circuit db to ground and theheaters are thereby cut off. If later he wishes to cut them in again, hepulls the button out. So long as the button remains in neither thethermostat nor the cut-out can exercise control to cut in the heaters.Another merit of myarrangement is that there is no interference with thenormal functioning of the thermostat control. So

long as the heater circuit is in its normal condition, the thermostatwill continue to cause the cutting off of the heaters when thetemperature of the car is too hi h and their cutting in when it is toolow. nly in the event of an accidental ground will the cut-out act andthen it will not affect the thermostat which will'resume its function assoon as the ground has been removed.

What I claim as new and desire to secure by Letters Patent is:

1. A safety device for electric heaters that are connected, in series,comprisinga main switch in the heater circuit, a switch-closingmagnetforsaid switch, a circuit shunting said closing magnet, a thermostatcontrollin said shunting circuit, a branch from said shunting circuit, aspring-closed switch in said branch, and a releasing magnet thereforhaving differential coils contained in the heater circuit on o positesides of the heaters.

2. A safety devlce for electric heaters that are connected in series,comprising a main switch in the heater circuit, a switch-closingmagnetfor said switch, a circuit shunting said closing magnet, a thermostatcontrolling said shunting circuit, a branch from said shunting circuit,a spring-closed switch in said branch, a releasing magnet thereforhaving diiierential coils contained in the heater 5 circuit on oppositesides of the heaters, and means including a manually cperable switch forindependently grounding said branch circuit, so as to shunt saidspring-closed switch. Signed at Albany, county of Albany and 10 State ofNew York, this 7th day of May, 1923.

LEE P. HYNES.

